Electronic timepieces in which various power generating means are mounted to supply energy for timepiece operation so that no exchange of batteries is necessary are already being commercialized. An electronic timepiece has been proposed in which, in order to further save energy, a portion of the circuit operations of the timepiece are frozen while the time information in the timepiece. FIG. 5 is a block diagram showing an example structure of a conventional power generating electronic timepiece.
Power generated by power generating means 1 such as a solar battery, a body temperature power generator, or an automatic winding power generator is charged to an electricity storage section 2 which is a secondary battery or a mass storage capacitor. The power is then supplied in a predetermined amount to the sections of a timepiece device 10 necessary to operate the timepiece, continuously in a small amount for counting time, or temporarily for driving a function which consumes a large amount of power, such as display illumination and an audio alarm. The timepiece device 10 includes the following circuits and devices.
A clock circuit 3 includes additional functions such as, for example, stopwatch and alarm. The clock circuit 3 outputs time information and various information for operating the additional functions as information resulting from a predetermined manipulation and calculation performed on a predetermined information, such as, for example, clock signal obtained from a reference frequency source, time signals of various periods produced based on the clock signal, and various values measured for the additional functions. A clock display section 5 includes a driving circuit for display, and displays the time information or information related to the additional functions produced by the clock circuit 3 through methods such as pointer (analog), digital display such as a liquid crystal, or alarm sound.
Power generation detecting means 100 includes a circuit for checking whether or not the power currently being generated by the power generating means 1 is greater than or equal to a predetermined level, and generates different outputs depending on whether or not the power is greater than or equal to the predetermined level (which is set at a level significantly lower than the normal level of power generation).
It may be thought that there is a direct correlation between the power level and usage state or environmental conditions of the timepiece such as, for example, the illumination of an optical power generating timepiece, difference between the temperature of the skin and the temperature of the atmosphere or the heat conduction state in a body temperature power generating timepiece, and strength of the movement in an automatic winding power generating timepiece.
Information processing means 4 receives output signals from the power generation detecting means 100 and, when the power generated by the power generating means 1 is at or exceeds a predetermined level, the information processing means 4 permits the time information and additional function information produced by the clock circuit 3 to drive the clock display section 5. Otherwise the information processing means 4 prevents transmission of this information. In the latter case, the clock circuit 3 continues to produce time information at a low power consumption, but the driving circuit in the clock display section 5 or the like which has a high power consumption is suspended, so that the timepiece device 10 enters a power save state. The arrow shown in the figure from the information processing means 4 to the power generation detecting means 100 indicates that the information processing means 4 in some cases generates a control signal for controlling the detection operation of the power generation detecting means 100. This corresponds to cases such as, for example, when the information processing means 4 suspends the detecting operation of the amount of power generated or when all the clock circuits are reset to the initial state.
Later, when the power generated by the power generating means 1 is restored to a level greater than or equal to the predetermined level, the display is also re-driven, although in a pointer type time display device, for example, there is a delay generated corresponding to the duration of the suspension. In light of this characteristic, the information processing means 4 includes a function to record the time when the display function is suspended due to decrease in the power generation and to drive the pointer in a fast forward motion to the correct current time at an early stage in time after the power is restored.
The predetermined power level is set at a level smaller than the power consumption of the timepiece device 10 and obtained by including a slight design margin in the level where it can be expected that continuation of the current level of power generation for a long period of time would cause the power charged in the electricity storage section 2 to decrease and the timepiece to eventually stop. The power level not only be indicated by the power itself, but can also be represented by other levels such as the voltage value level or the output current level generated by the power generating means. These values cannot only be measured instantaneously, but also by average value or accumulated value within a predetermined period until the current time.
The power generating means of the power generating electronic timepiece is designed so that sufficient power is generated under a normal usage condition. Therefore, by configuring the timepiece as above, for example, when a timepiece with an optical power generating device is stored and left in a drawer of a desk or the like (display of time and other functions would not be necessary for this time period), the timepiece enters the power save state as described above. When later the timepiece is taken out and is worn on the arm in a bright environment, the timepiece returns to the normal operation state and sufficient power to charge the battery is again generated. Therefore, because of the characteristics that no battery exchange is necessary and that the time need not be manually adjusted, a power generating timepiece is provided which has less restriction on the usage and without a restriction that the same timepiece must be always used.
Another conventional power generating electronic timepiece is equipped with a charge alarm display function. This function monitors the charge voltage of the electricity storage section and, when this voltage falls below a predetermined voltage detection value, the display is switched from normal display to a charge insufficiency alarm display (modulated display is performed). Japanese Patent Publication No. Hei 7-46145 discloses an art where hysteresis is provided for the voltage conditions for changing the display state which depend on the direction, wherein different voltage detection values of the electricity storage section are used in situations when switching from the normal display to the charge alarm display and when switching from the charge alarm display to the normal display.
In the prior art shown in FIG. 5, the power level for suspending a portion of the functions of the electronic timepiece due to decrease in the amount of power generated and the power level for restoring all functions due to increase in the amount of power generated are set at the same level. No significant problem arises if there is a sufficient difference between the power generation level in the normal operation state of the electronic timepiece and that in the power save state. However, the actual usage condition is not ideal, and there are cases where the power generation level fluctuates around the predetermined power level. When the timepiece is restored from the power save state to the normal operation state, a process, such as an operation for fast forwarding the pointer to the current time, is performed which consumes a large amount of energy.
Thus, when the power generation is at a low level and varies, frequent switching occurs and the power consumption in fact becomes large, resulting in negation of the intended power save effect. This may happen, for example, when the timepiece is moved between under the cloth and under no cloth or when the room illumination changes for a timepiece having a solar cell in the dial, when the contact with the skin changes for a body temperature power generating timepiece, and when the timepiece is used with small motion for a timepiece with automatic winding power generator.
The art disclosed in Japanese Patent Publication No. Hei 7-46145 described above is an art for warning of a charge insufficiency state, and not an art for saving power. An application of this prior art may enable switching of the timepiece between the normal state and the power save state by monitoring the charge voltage of the electricity storage section, but, even if the timepiece is switched to the power save state after the charge power in the electricity storage section is clearly decreased, it is highly probable that the remaining power is insufficient to drive the timepiece for a long period of time, and, thus, a power save function which is practical cannot be obtained.
One object of the present invention is to provide a power generating electronic timepiece and control method of such an electronic timepiece in which the switching process between a first state (for example, a normal state) and a second state (for example, a power save state) is improved in order to prevent frequent state change in a timepiece due to a small change in the amount of generated power, for example, when power is not generated or when power is generated at a low level, resulting in increased stability (for example, increased power save effectiveness) of the timepiece operation.